This invention relates to needles and, more particularly, to needles used with plastic fasteners in order to insert the fasteners into objects to be marked or attached.
Needles of this type are disclosed in U.S. Pat. Nos. 3,470,834, 3,759,435, Re. 29,310, Re. 29,819, and 4,039,078, all issued in the name of Arnold R. Bone and assigned to Dennison Manufacturing Company. Such needles are especially designed to dispense plastic fasteners of the type disclosed in U.S. Pat. No. 3,103,666 (see FIG. 2, showing one such needle), including on at least one end a cross-bar or T-bar joined to a thin, strong filament. Where T-bars are provided at both ends of the filament (or "connector"), as in U.S. Pat. No. 4,039,078, two needles are provided, one for each T-bar. Such needles include a central bore to guide the T-bar, and a longitudinal slot to guide the filament, of a fastener to be dispensed. In addition, these needles can have a cutter included as an integral part of the needle design, or the needle can be designed without a cutter, in which case a knife or cutting surface would be included separately to provide the cutting function.
Needles of the prior art are typically made by relatively involved machining processes. For example, one typical method of manufacturing a needle involves taking a solid metal cylindrical blank, or workpiece, with a point at one end and machining a longitudinal groove down one side of the blank. The groove is then compressed, or clinched over, in order to form sidewalls which will guide the filament of a plastic fastener. The problem with this type of needle is that the groove's sidewalls do not have the proper configuration to provide the necessary guidance.
When the groove is clinched over, the originally parallel sidewalls are canted toward each other, resulting in angled sidewalls which provide minimal contact surface for the fastener filament passing through the needle. These angled sidewalls allow the cross-bar of the fastener to be pulled away from the center of the needle. In addition, the surface texture of the resulting sidewalls do not typically have the smoothness required to ensure easy passage of a fastener filament. In fact, the needle sidewalls often are so rough as to contribute to breakage of the fastener filaments during application.
Another problem is that the diameter of the front portion of the needle tip is not optimized relative to the diameter of the central bore through the needle. This causes the material of the object being penetrated by the needle to impinge upon the fastener, especially in the vicinity of the junction of the cross-bar with the filament of the fastener. This impingement adds enough stress to the junction area to cause breakage in too many cases.
Still another problem exists in the configuration of the needle at the critical area where the central bore and longitudinal slot merge into the tip portion. The configuration of the prior art allowed this critical area to actually serve as somewhat of a cutting edge by adding sufficient stress to the fastener cross-bar and filament junction to cause breakage, similar to the effect of cutting through the filament near the junction with a knife.
Accordingly, it is an object of the invention to provide a needle having more consistent dimensions than those of the prior art. More specifically, it is an object of the invention to provide groove sidewalls which have an appropriate configuration and adequate physical dimensions, as well as an adequately smooth surface texture, to facilitate the insertion of plastic fasteners into desired objects without breaking the filaments of the fasteners.
A further object of the invention is to optimize the diameter of the front portion of the needle tip relative to the diameter of the central bore through the needle in order to minimize unnecessary stress which results in breakage of the fasteners.
A still further object is to provide a proper configuration for the critical area where the central bore and the longitudinal slot merge into the tip portion of the needle in order to minimize the possibility of this area acting as a cutting edge on the fastener.